SUMMER-2015 Examination Subject Code: Model Answer : Applied Science (Chemistry) Page No: 1/14 Que. No.

Transcription

1 Subject Code: 7 : Applied Science (Chemistry) Page No: / Important Instructions to examiners: ) The answers should be examined by key words and not as word-to-word as given in the model answer scheme. ) The model answer and the answer written by candidate may vary but the examiner may try to assess the understanding level of the candidate. 3) The language errors such as grammatical, spelling errors should not be given more Importance (Not applicable for subject English and Communication Skills). ) While assessing figures, examiner may give credit for principal components indicated in the figure. The figures drawn by candidate and model answer may vary. The examiner may give credit for any equivalent figure drawn. 5) Credits may be given step wise for numerical problems. In some cases, the assumed constant values may vary and there may be some difference in the candidate s answers and model answer. 6) In case of some questions credit may be given by judgement on part of examiner of relevant answer based on candidate s understanding. 7) For programming language papers, credit may be given to any other program based on equivalent concept.

2 Subject Code: 7 Page No: /. Attempt any NINE of the following: 8 a) Write the two ores of Copper with their chemical formula. Type of ore Name Chemical formula Oxide Cuprite or ruby copper Cu O Sulphide Copper glance Cu S Copper pyrite CuFeS Carbonate Malachite CuCO 3,Cu(OH) Azurite CuCO 3,Cu(OH) ( Any two ores of Copper with formula: mark ) b) c) What are the constituents of copper matte. Constituents : Mixture of molten Cu S( Copper sulphide ) FeS(Ferrous sulphide) traces. Write two uses of aluminium. ) For preparing utensils, surgical instruments, heating appliances, parts of aeroplanes, containers for chemical industry etc. ) For making electric wires and cables for transmission lines. 3) Aluminium foils are used for wrapping cigarettes, sweets and confectionary. ) Al powder is used for making silvery paints. 5) As a reducing agent in the production of Cr, Mn etc. 6) In thermite welding process. 7) As a deoxidizer in the manufacture of steel. 8) For winding the moving coils of dynamos and motors. 9) Highly pure Al is used as an absorber in the preparation of antibiotics (chloromycines). 0) Al powder + NH NO 3 mixture is used in bombs. ) For making many useful alloys. ) For chemical plants and transporting and storing nitric acid. 3) As refractory for lining of furnace and for making refractory bricks.

3 Subject Code: 7 Page No: 3 /. d) e) Define immersed corrosion. Definition: The corrosion which is brought about through ionic reactions in the presence of moisture or solution as a conducting medium when two dissimilar metals are in contact with other is called electro chemical corrosion. State the two functions of pigment. ) Provide opacity and colour to paint film. ) Give strength to the film. 3) Give protection to the paint film by reflecting harmful ultraviolet light. ) Provide resistance to paint film against abrasion, moisture and weather. 5) Give an aesthetical appeal (i.e pleasing to look at) to the paint film. (Note: Any two functions) f) Draw neat and labelled diagram for application of metal on an article by galvanizing process. g) What are applications of sherardizing process?(two points) Applications:- i)sherardizing is used especially for protecting small odd shaped steel articles like bolts, screws, nuts, threaded parts washers, valves, gauge, tools etc.against atmospheric corrosion. ii) The main advantage of sherardizing is that coating is quite uniform even if the surface has crevices or depression and there is practically no change in the dimensions of articles.

4 Subject Code: 7 Page No: /. h) Define the terms:i)specific conductance ii) Equivalent conductance i)specific conductance (k) : Specific conductance is the conductance of a cm 3 of the substance or solution. OR The conductance offered by a solution of unit length & area of unit cross section is known as specific conductance. ii) Equivalent conductance ( v) : It is the conductance of the solution containing gm equivalent of solute / electrolyte when placed between two sufficiently large electrodes cm apart. i) Write two points to differentiate between primary cell and secondary cell Primary cell Secondary cell. Non- rechargeable cells. Rechargeable cells are are known as primary cells. known as secondary cells.. Chemical reaction is. Chemical reaction is irreversible. reversible. 3. They are light in weight. 3. They are heavy.. They have short life.. They have long life 5. They can not be recharged 5. They can be recharged & & reused. reused. 6. e.g. Dry cell, Daniel cell, 6. e.g.lead acid storage cell, Leclanche cell. Nickel- cadmium storage cell (Any two points) j) k) State two uses of electrically conducting polymer. They are used in rechargeable batteries They are used as analytical sensors to detect ph, O,NO, SO,NH 3, glucose etc 3. They are used as antistatic materials in offices, theatres etc.. They are used as electro chromic materials 5. They are used in optical filters to absorb radiations from computer, T.V. screens. 6. They are used for photo diodes, light emitting wall papers, light emitting diodes &data storage. 7. They are used in construction of photo voltaic cell (Any two uses) State two applications of silione fluids.

5 Subject Code: 7 Page No: 5 /. Applications:- ) As a lubricant: excellent lubrication for plastic and elastomeric surfaces. )In polishes and chemical specialities: It is used in automobile and furniture polishes due to its high gloss and water repellency. 3) As a mechanical fluid: It is used as hydraulic or transformer oils, damping mediums. ) As coolant: They are used as coolant in radio, pulse and aircraft transformers. 5) As a foam preventive: effectively control foam in many machines like photocopiers and laser printers. 6) Also used in cosmetic and pharmaceutical industries. 7) In electrical and chemical specialities: Used as an insulator in medium and high voltage applications i.e. in transformers. 8) As a release material : an odourless,non-toxic, noncarbonizing moulds release for rubber, plastics and metal die castings. l) Write two applications of phenol formaldehyde resin as an adhesive. ) Used as adhesive for grinding wheels & brake linning. ) Used for decorative laminates wall covering & industrial laminates for electrical parts. 3) Used for making water-proof plywoods. ) Used in bonding articles in air craft and ship building.

6 Subject Code: 7 Page No: 6/. a) s Attempt any FOUR of the following: How copper is obtained from its ore by smelting process? Write it with labeled diagram. 6 Process: i) Roasted copper ore is then mixed with coke & sand particles & then strongly heated at high temperature in a water jacketed blast furnace. ii)at high temperature ferrous sulphide (FeS) is oxidised & converted into ferrous oxide (FeO) which further reacts with sand particles to form a fusible slag (FeSiO 3 ) FeS +3O FeO + SO FeO + SiO FeSiO 3 iii) Further cuprous oxide (Cu O) formed during roasting combines with ferrous sulphide (FeS) to form ferrous oxide (FeO) & cuprous sulphide (Cu S). The ferrous oxide (FeO) formed futher react with silica particals to form slag. Cu O + FeS FeO + Cu S iv) Thus during smelting process most of the ferrous sulphide impurity is converted into the fusible slag (FeSiO 3 )which is then removed from the upper slag outlet. v)the molten mass containing mostly cuprous sulphide (Cu S) & little quantity of ferrous sulphide (FeS) is called as matte which is then removed from the lower outlet. b) Write the purification of aluminium with labelled diagram by electroytic refining.

7 Subject Code:7 Page No: 7 /. s Process: ) The electrolytic cell consists of an iron tank lined at the bottom with carbon, which serve as anode. A number of graphite rods serve as cathode. ) The cell is filled with three liquid layers of different densities. i)the top most layer consists of molten pure aluminium which acts as cathode. ii) The middle layer is of electrolyte which consist of a mixture of molten fluorides of Al, Ba & Na. iii) The bottom layer consists of molten impure aluminium. 3) On passing electric current, the aluminium ions from the middle layer discharged at the cathode and get collected in the top most layers. Same amount of aluminium ions from the bottom layer goes into the middle layer. Pure Al collected at the top is tapped out from time to time. Crude or impure Al is added to the bottom layer from time to time. The process is thus continued. 3 c) State composition properties and applications of Tinmann s solder or rose metal Solder Composition Properties Applications Tinmann s solder: Rose metal Sn = 66 % Pb = 3 % Bi = 50% Pb = 8% Sn = %. It melts at 80 0 C..It is easily fusible alloy.. Its melting point is 89 0 C It is used for joining articles of tin.. It is used for making fire alarms. It is used in electrical fuse wires, 3. It is used for casting for dental works. It is used in automatic sprinkler system.

8 Subject Code: 7 Page No: 8/. (Note: mark for composition,mark for properties, mark for applications for any one alloy ) d) Write four properties and applications of urea-formaldehyde resin. Properties : ) The bond film produced by urea formaldehyde resin is quite rigid & transparent. ) It is good resistant to moisture, insects & fungi. 3) However action of acids & alkalies deteriorate the resin film after some time. ) It can be used in cold but a little heating helps in accelerating the setting process. Applications: (Any two) ) Used for bonding wooden surfaces. ) Used for bonding water proof plywood, laminates. 3) Bonding articles in aircraft & ship building industries etc. e) Give construction, working and application of Dry cell. Construction:It consists of zinc container (vessel) which acts as an anode.cathode is a Graphite rod. It acts as inert electrode. The Graphite rod is surrounded by a paste of MnO (Manganese dioxide) & powdered Carbon (Black).The cell is filled with a paste of NH Cl & ZnCl prepared in water. The cell is sealed at the top by wax or resin. Working At zinc anode: - Dissolution of zinc electrode to form zinc ions. Zn Zn ++ + e - (oxidation) Zn + combines with ammonia to form its complex. Zn NH 3 Zn (NH 3 ) At the graphite cathode: - Manganese dioxide (MnO ) reaction with NH + (ammonium) ions to liberate ammonia. NH + + MnO + e - Mn O 3 + H O + NH 3

9 Subject Code: 7 Page No: 9/. Ammonia thus produced is liberated as a gas but it combines with Zn + to form a Zn (NH 3 ) ++ ions complex at the zinc anode. Application: ) The dry cell useful for small amount of current required for short period of time. ) Dry cells are used in torches, transistors, tape recorders, door bells, gas engine ignition, wall clock, T. V. remote.c. 3) The cell develops a potential.5 volts. (Any one application mark) f) Write reactions taking place during charging and discharging of lead acid storage cell. Discharging: - At Anode: - Pb Pb + + e ( Oxidation) Pb + + SO - PbSO At Cathode:- PbO + H + + e - Pb + + H O (Reduction) Pb + + SO - PbSO Net reaction during Discharging: - Pb + PbO + H + + SO - PbSO + H O Charging: - At Cathode: PbSO + e - Pb + SO - At Anode: PbSO + H O PbO + H + + SO - + e - Net reaction during Charging: PbSO + H O Pb + PbO + H + + SO - [Note: mark to be given to reaction at anode & cathode] 3. a) Attempt any FOUR of the following: Define atmospheric corrosion. Write mechanism when oxygen attacks on a metal. 6 Atmospheric corrosion: This type of corrosion occurs when metal surface comes in immediate contact directly with atmospheric gases like O, Cl, Br, I, H S, CO, SO, NO etc. Mechanism: Metallic surfaces when exposed to air undergo oxidation and the process of corrosion is represented by the eq n. M + O MO (Metal Oxide) (Metal) (Oxygen)

10 Subject Code: 7 Page No: 0/ 3. A thin oxide layer is formed on the metal surface and the nature of this film decides further action depending upon the film so produced. M M + + e (loss of electrons) ( Metal ion) O + e O (gain of electrons) M + O M + + O MO (Metal oxide) b) Describe the hydrogen evolution mechanism of immersed corrosion. Steel tank: - Anode, Cu strip:- Cathode These types of corrosion occur usually in acidic environments like industrial waste, solutions of non oxidizing acids. Process: A steel tank containing acidic industrial waste and small piece of copper scrap in contact with steel. The portion of the steel tank in contact with copper is corroded most with the evolution of hydrogen gas. At anode Fe Fe ++ + e (Oxidation) These electrons flow through the metal from anode to the cathode At cathode H + ions are eliminated as H gas H + + e H (Reduction) Thus, over all reaction is Fe + H + Fe ++ + H [Note: mark to be given to reaction at anode & cathode.]

11 Subject Code: 7 Page No: / 3. c) Model answers Describe metal spraying process for protection of metal from corrosion.write its two applications. Process:-i) In this method, coating metal sprayed on the surface of base metal with the help of spraying gun or pistol. ii) The spraying gun consist of a duct for compressed air and is fitted with the oxy- hydrogen flame. iii) The coating metal in the form of wire is fed into the gun which is then melted inside the gun with the help of oxy hydrogen flame. iv) The molten metal then sprayed on the surface of base metal with the help of compressed air. Applications: (Any Two) ) Can be applied to non metallic bases made of wood plastic and glass. ) Coating can be applied to fabricated structure. 3) Worn-out out machine parts can be reclaimed. ) Coating of metals like Al, Zn, Ni, Sn, Pb etc. is made by the method of spraying. (Note: mark should be given if diagram is drawn) d) Write construction and working of Ni-Cd cell with labelled diagram. OR Construction: i) Positive plates are made up of nickel plated tubes, containing a mixture of nickel oxide (NiO ) & hydroxide + 7% flakes of graphite or metallic nickel for increasing conductivity. ii)they also contain an activated additive % Ba(OH) which increases the life of plates. Negative plates consist of spongy Cadmium.

12 Subject Code:7 Page No: / Model answers 3. iii) The electrolyte is 0-5% solution of KOH to which small quantity of lithium hydroxide (LiOH) is added to increase the capacity of cell. Working: A) Discharging:- Positive Plate: NiO (s) + H O (l) + e Ni (OH) (s) + OH Negative Plate: Cd (s) + OH (aq) Cd (OH) (s) + e Net reaction: NiO (s) + Cd(s) + H O Ni(OH) + Cd(OH) B) Charging:- Positive Plate: Ni(OH) (s) + OH (a) NiO (s) + H O + e Negative Plate: Cd(OH) (s) + e Cd(s) + OH(s) Net reaction: Ni(OH) + Cd(OH) NiO (s) + Cd(s) + H O Thus, discharging & charging reactions can be shown simultaneously as: - NiO (s) + Cd (s) + H O Ni(OH) + Cd(OH) OR A) Discharging:- Positive Plate: NiO(OH) + H O + e Ni (OH) + OH Negative Plate: Cd + OH Cd (OH) + e Net reaction: NiO(OH)+ Cd + H O Ni(OH) + Cd(OH) B) Charging:- Positive Plate: Ni(OH) + OH NiO(OH) + H O + e Negative Plate: Cd(OH) + e Cd + OH Net reaction: Ni(OH) + Cd(OH) NiO(OH) + Cd+ H O Thus, discharging & charging reactions can be shown simultaneously as: - NiO(OH) + Cd (s) + H O Ni(OH) + Cd(OH)

13 Subject Code:7 Page No: 3/ 3. e) Model answers Give Construction and working of hydrogen-oxygen fuel cell Construction :- i)one of the simplest & most successful fuel cell is hydrogen oxygen fuel cell. ii) It consists essentially of an electrolytic solution such as 5% KOH or NaOH solution, & two inert porous electrodes (like porous carbon) containing suitable catalyst. iii) Hydrogen & oxygen gases are bubbled through the anode & cathode compartment respectively. Working: - At anode: - H + OH - H O + e - At cathode: - O + H O + e - OH - Net Reaction: H + O H O [Note: mark to be given to reaction at anode & cathode.] f) Write discharging and charging process of lead acid storage cells. i) Discharging: - While discharging chemical energy gets converted into electrical energy. At Anode: - Pb Pb + + e ( Oxidation) Pb + + SO - PbSO At Cathode:- PbO + H + + e - Pb + + H O (Reduction) Pb + + SO - PbSO Net reaction during discharging: - Pb + PbO + H + + SO - PbSO + H O

14 Subject Code:7 Page No: / Model answers 3. Lead sulphate is precipited at both the electrodes. The voltage of cell is.0 volts at 5 o C because the concentration of sulphuric acid varies from 5% to 0%. ii) Charging: - To recharge a lead storage cell, the reactions taking place during discharging are reversed by passing an external e.m.f. greater than volts from a generator. At Cathode: PbSO + e - Pb + SO - At Anode: PbSO + H O PbO + H + + SO - + e - Net reaction during Charging: PbSO + H O Pb + PbO + H + + SO - During the process of charging, the electrodes of the cell are restored to their original conditions (to Pb and PbO respetively).